Microscopes Flashcards
Describe what is meant by the magnification of an object
- How many times bigger an image appears than it’s actual size
What is the material that is placed under a microscope called
- An object
What is the appearance of the material when viewed under a microscope called
- An image
What are the two types of microscopes called (GCSE)
- Optical microscope
- Electron microscope
Describe what is meant by the resolution/resolving power of a microscope
- The minimum distance apart that two objects can appear as separate objects
The smallest organelle that can be viewed by a microscope is determined by:
A) Magnification
B) Resolution
- Resolution
Why does increasing the magnification sometimes result in a blurry image
- Beyond the limit of resolution, increasing the image further will result in the image looking blurry
Why can’t organelles like mitochondria be seen under an optical microscope
- The mitochondria is too small and the resolving power (resolution) is too low
A student cannot see the organelles of a red blood cell, explain why
Red blood cell has no organelles because their cytoplasm is filled with hämoglobin
What are the 3 types of microscopes you need to know about at A-level
- Optical microscope
- Scanning electron microscope (3D image)
- Transmission electron microscope (2D image)
What is the radiation source for optical microscopes
Light
What are the 2 lenses in a light microscope called
- Objective lens
- Eyepiece lens
What is the maximum magnification in a light microscope
X1500
How do you calculate the total magnification of an optical microscope
Eyepiece X objective
What is the maximum resolution in a light microscope
200nm
State the advantages of an optical microscope
- produce coloured images
- view live specimens
- portable
Describe what happens in a transmission electron microscope
- Electrons pass through the thin specimen
- Denser parts absorb more specimen
- Therefore denser parts appear darker
What is the radiation source for transmission electron microscopes
Electrons
Why do electron microscopes have a higher resolution than light
Shorter wavelength
What causes parts of the image to appear darker in transmission electron microscopes
Denser parts absorb more electrons, therefore they appear darker
What causes parts of the image to appear lighter in a transmission electron microscope
Less dense parts transmit electrons
Describe what happens in a scanning electron microscope
- Electrons are scattered off the surface of the specimen, and so they produce a 3D image
State the advantages of electron microscopes (TEM & SEM)
- Scanning electron microscopes allows us to see 3D images
- Transmission electron microscopes have the greatest resolving power (resolution), which allows us to see the smallest organelles
State the disadvantages of electron microscopes (TEM & SEM)
- The specimen must be dead as it’s placed in a vacuum
- The specimen must be extremely thin and there is a complex staining process, which is time consuming to prepare
- Artefacts: defects in images caused by errors in preparation, therefore it’s difficult to tell if they’re part of the real object or not
What is the maximum magnification of a TEM and SEM
X 500,000
What is the maximum resolution for a TEM
0.1nm
What is the maximum resolution for a SEM
20nm
Explain why some organelles could be
seen with a transmission electron microscope
but not with an optical microscope.
An electron microscope has a higher resolution; as electrons have a shorter wavelength.
